Hypertension, or high blood pressure, is the most prevalent cardiovascular disease, afflicting nearly one in every three American adults. The prevalence of this disease is even higher in African-Americans but the underlying cause is unknown. Atrial natriuretic peptide (ANP) is a cardiac hormone. When blood pressure increases, ANP is released from the heart to promote renal sodium and water excretion and decrease peripheral vascular tension, thereby lowering blood pressure. In cardiomyocytes, ANP is made as a precursor, pro-ANP, which is activated to ANP by a proteolytic enzyme. This activation step is critical in regulating ANP activity but the processing enzyme remained elusive for many years. Recently, we discovered a cardiac serine protease, corin. We showed that corin activated pro-ANP in a sequence-specific manner. We made corin-deficient mice in which pro-ANP activation was abolished, demonstrating that corin is the physiological pro-ANP convertase. Corin-deficient mice develop hypertension that was exacerbated by a high-salt diet, indicating that corin is essential in maintaining normal blood pressure. Corin also cleaved pro-B-type natriuretic peptide (BNP) in vitro. Most recently, non- synonymous single nucleotide polymorphisms (SNPs) in the corin gene are found to be associated with hypertension and cardiac hypertrophy in African-Americans. In this proposal, we will test the hypothesis that the SNPs alter corin function and contribute to hypertensive and heart disease. In Aim 1, we will examine corin and its variants in pro-ANP and pro-BNP processing in biochemical and cell-based assays. In Aim 2, we will examine the molecular mechanism in corin activation. In Aim 3, we will determine the role of corin and its variants in natriuretic peptide processing, blood pressure regulation, and cardiac hypertrophy in mouse models. Our studies will help to elucidate the function and regulation of this newly-discovered enzyme and, more importantly, to understand if corn deficiency plays a role in hypertensive and heart disease. Our studies may help to design new strategies to diagnose and treat patients with hypertension and heart failure. PUBLIC HEALTH RELEVANCE: Nearly one in every three American adults develops high blood pressure, also called hypertension, a disease that can cause stroke and heart attack. This disease is even more common in African-Americans than in the general population, but the exact cause is not known. We discovered a new protein, corin, from the heart that is important in keeping normal blood pressure. Recently, corin gene variants are found in African-Americans with high blood pressure and heart disease. In this study, we will do experiments to figure out if corin gene changes cause blood pressure and heart problems. Our work will help to develop new ways to diagnose and treat patients with high blood pressure and heart disease.